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Old 08-16-2007, 10:28 AM   #16 (permalink)
 
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Why did you go ahead and do toe-in in the rear? I still haven't seen any other Evo racer do that. I think -1.8 camber in the rear is too much, too. Where did you come up with the settings you chose?

More toe-out up front gives better turn-in. I am not a guru, though, so I can't explain the engineering behind it.





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Old 08-16-2007, 12:51 PM   #17 (permalink)
 
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Simple. I had consulted several decent sources on the toe-out debate:

1. the settings were provided by an engineer for Whiteline who uses these settings on their demo cars used for track.

2. leading UAE autocrossers had the same recommendation -- toe-in for extra stability when dealing with nasty high speed corners for track, toe-out being a preferred setting for autocross

3. a track regular mate of mine back in Singapore had also recommended going toe-out on the front and toe-in on the rear, for better turn-in and improved rear end stability

I've tested this in a 'safe' environment around here and have found that the rear sway bars took away a little bit of the snappy rear end behaviour and replaced it with throttle-controllable rear end movement. Based on this feedback, I guess it also boil down to what the driver is used to.

For example, you're pretty much a god at autocross relative to say, track. That's not to say that you're not good at track, but autocross may be more of your thing. As a result of that preference, you may have gone with negative toe on the rear for so long that handling a car set up as such it becomes second nature to you, and you may not perform as well if you were to run any more positive to than you have now.

But we do agree on one thing: Toe-out on the front improves toe-in.

Question is, as with any form of tuning, there's always a trade-off. What have I given up by using negative toe on the front? Braking distance? Braking stability? High-speed front-end instability?

Guess that's something to think about...
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Old 08-16-2007, 05:48 PM   #18 (permalink)
 
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Actually, no, my entire setup is 100% optimized for nationally competitive road racing (time trials) and was developed over the course of 2 years by a professional racer named Paul Gerrard. He developed this setup on his own Evo on local tracks and through pure science with the help of the FSAE team in the Mechanical Engineering program at Colorado State University. They used an in-house shock dyno to determine perfect valving and used all sorts of sophisticated logging equipment on the car while on track using all combinations of camber, toe, spring rates, valving, etc etc. At the end of the 2 years, they put the package together through Vishnu and started selling it. It didn't last long, because Ohlins USA couldn't keep up with the demand, so only a small group of us actually have these, and even fewer have my extreme spring rates (700lb/900lb = ~12kg/16kg).

So, my setup is SPECIFICALLY for dominant performance on track, and it's a combination of the package itself as well as precise alignment settings, corner balancing, ride height, etc., all done by the same team in that same facility where all the engineering was performed. I just happen to also use this same setup for autocrossing, but I consider myself much better on track than in autocross. I don't even like autocross, but it's very cheap and takes up less time, so that's what I do more of due to having a 1yo. If I didn't have a kid, I'd be headed to Ohio in a few weeks for the NASA National Time Trial competition with an expectation of placing pretty high in my class.

I didn't want you to think my setup, my experience, or my abilities were specific to autox. Everything I've been telling you was specific to track setup, not autox. At no point in time was toe-in a suggestion, recommendation, nor even a topic of discussion. It's interesting that the folks you've talked to on that side of the world keep mentioning. It is not something I've seen on this side of the world, so it probably works as part of a system designed for it. I couldn't tell you if one way is faster than another. All I know is that I gained 6 seconds on the same track after adding my suspension and using this setup along with 285-width V710s. The time I ran was absurdly fast relative to others who run on this course. The only car that was faster was a 500HP Noble M12 practicing for One Lap of America - he was 2 seconds faster on his best lap.





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Old 08-16-2007, 11:46 PM   #19 (permalink)
 
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My goodness. We really don't get this sort of setups available on this side of the world. Indeed, I wish we did, because it appears that your car is running at pretty much the same level of power, and the difference would probably be in how the suspension is set up (and thus, driver, ie. me, being the limiting factor)

That said, I would try out the settings that are on the car now (since none of the alignment shops are open on Friday - a holy day in the Middle East) and switch over to your recommendations for the next one to try out the difference. After much thought it probably doesn't make sense to continue pouring money into the Evo to get it up there as a competitive track machine, given that (and again, like you, I have other priorities that demand my time, effort and finances in life) a Radical PR6 would cost me as much as I have put into the Evo. In the longer term, I would probably just sell the Evo, get a beater that I can hook up a small trailer to and use the Radical for track work instead. If I were in the US, a Skip Barber Driving School would probably be on the list before the Radical, but alas, I'm not heading up anytime soon (unless I can convince the missus that the US would be a great place for a honeymoon).

In the meantime, all I'll be doing is making small improvements to the suspension and alignment settings and be as competitive as I can. Thanks for the help
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Old 08-17-2007, 10:54 AM   #20 (permalink)
 
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Feedback from the track evening.

I just clocked in one of the fastest lap times for a car on street tires on the Dubai Autodrome -- 1:20.8 min. What was important, however was how the car behaved:-

1. First 20-minute session - I was all over the place. Car was NOT responding very well. Loads of understeer, and the rear stubbornly refused to let go unless really provoked. Wasn't slow, but it wasn't behaving the way I wanted.

Got back to the pit garage, and checked tire pressures. My 38f/40r ended up becoming 44f/46r after 15 laps. At a friend's advice, I dropped hot tire pressure down to what you recommended : 38f/40r, and went out for the 2nd session

2. 2nd 20-minute session - MUCH, MUCH BETTER. front end tracked so nicely, I could get the car into a 4-wheel drift (slightly) in order to get a better exit angle past the apexes. Rear end was still a stubborn and would scrub in some corners when provoked, but at least it would rotate better.

3. 3rd and last 20-minute session. Didn't intend to go balls-out, but ended up being followed by what I had thought was a stock standard white Golf Mk V GTI. I could barely stay ahead, and eventually decided to let him pass, only to find that it was a Golf GTI Cup car (semislicks, stripped out, roll cage, tuned, etc - was later told that it was not just a Cup car, but was also modified to 350 whp), driven by a Cup driver as well (Golf GTI Cup is an FIA-sanctioned event). Ended up following it as best as I could and unwittingly clocked 1:20.8 (I wasn't timing, but found out after the event that a friend who decided to swing by was clocking me from the pits)

Anyway, lesson learnt tonight - car is not slow, rear camber needs to be dropped from -1.8 to -1.2 deg, and I'm doing to run slightly less positive camber (probably 0.03 toe-in), but I am so tempted to either increase the stiffness of the rear sway bar (my god, they DO help -- car rotates more predictably, for some reason), or run a bit of toe-out.

Warr, thanks for the advice. let me know what you think comes next -- run toe-out (0.02mm toe out per side on the rear) or run stiffer rear sway bar, or both?
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Old 08-17-2007, 11:49 AM   #21 (permalink)
 
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I'm not knowledgeable enough to give those types of details. I'm still learning how to react to my own car. It would be nice if we did have people here who understood the science behind such things, but they're not easy to find.





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Old 08-17-2007, 01:20 PM   #22 (permalink)
 
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I agree with you.

Warr, I want to thank you for the invaluable advice you provided in the earlier posts. I'm going to the alignment shop tomorrow and get either or all of the following done:

1. slight toe-out (0.03 mm per side)
2. set rear sway bar to the stiffest setting
3. increase negative camber to -1.3 deg

What I have noticed with the current setup is that I am now able to take long sweeping corners at ridiculously high speeds, at least 20 to 25 kmph more than when I was running pretty much the settings above, save for the sway bar setting.

This probably needs a bit more thought overnight...
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